In-situ annealing and etch back steps to improve exchange stiffness in cobalt iron boride based perpendicular magnetic anisotropy free layers

ABSTRACT

A method for forming a memory device that includes providing a free layer of an alloy of cobalt (Co), iron (Fe) and boron (B) overlying a reference layer; and forming metal layer comprising a boron (B) sink composition atop the free layer. Boron (B) may be diffused from the free layer to the metal layer comprising the boron sink composition. At least a portion of the metal layer including the boron (B) sink composition is removed. A metal oxide is formed atop the free layer. The free layer may be a crystalline cobalt and iron alloy. An interface between the metal oxide and free layer can provide perpendicular magnetic anisotropy character.

BACKGROUND Technical Field

The present invention relates to magnetic random access memory devicesand apparatuses, and more particularly to increasing the magneticexchange stiffness of material layers used in magnetic random accessmemory devices.

Description of the Related Art

Magnetic random access memory (MRAM) devices differ from conventionalrandom access memory (RAM) in that data is stored through the use ofmagnetic elements as opposed to storing data through electric charges orcurrent flows. In accordance with MRAM, two magnetic elements areseparated by a barrier. In addition, one of the magnetic elements can bea permanent magnet set to a fixed polarity while the polarity of theother magnetic element is adaptable to store data. The different digitalstates (i.e. one or zero) can be differentiated by assessing whether thepolarity of the two elements are the same or different. Data can be readby measuring the electrical resistance of the cell. For example, atransistor can switch a current through the cell such that chargecarriers tunnel through the barrier in accordance with the tunnelmagneto resistance effect. The resistance of the cell is dependent onthe magnetic moments of the two elements. Writing data in an MRAM can beconducted using a variety of methods. Spin transfer torque (STT), whichemploys a spin polarized current, is one such method.

In accordance with STT, the spin-polarized current is altered as itpasses through the adaptable magnetic element, thereby applying a torqueto the magnetic element and changing its polarity. Further, there aremultiple types of STT MRAM devices. For example, reference layers andfree layers of in-plane STT MRAMs have magnetic moments that areparallel to the wafer plane. Alternatively, reference layers and freelayers of Perpendicular Magnetic Anisotropy (PMA) STT MRAMs havemagnetic moments that are perpendicular to the wafer plane.

SUMMARY

In one embodiment, a method is provided for forming a memory device thatincludes providing a free layer of an alloy of cobalt (Co), iron (Fe)and boron (B) overlying a reference layer. A metal layer comprising aboron (B) sink composition may be deposited atop the free layer. Ananneal process diffuses boron (B) from the free layer to the metal layercomprising the boron sink composition. At least a portion of the metallayer including the boron (B) sink composition is removed. A metal oxideis formed atop the free layer, wherein the free layer comprises acrystalline cobalt and iron alloy and an interface between the metaloxide and free layer provides perpendicular magnetic anisotropycharacter.

In another embodiment, a method is provided for forming a memory devicethat includes providing a free layer of an alloy of cobalt (Co), iron(Fe) and boron (B) overlying a reference layer. A metal layer comprisinga boron (B) sink composition may be deposited atop the free layer. Ananneal process diffuses boron (B) from the free layer to the metal layercomprising the boron sink composition. The metal layer including theboron (B) sink composition is removed. An alloy layer of cobalt and ironis formed atop an exposed surface of the free layer. A metal oxide isformed by oxidation anneal atop the free layer. The free layer comprisesa crystalline cobalt and iron alloy and an interface between the metaloxide and free layer provides perpendicular magnetic anisotropycharacter.

In another aspect, a memory device is provided that includes a magnesiumoxide tunnel layer atop a reference layer, and a crystalline free layercomprised of cobalt and iron alloy that is substantially free of boron,wherein the crystalline free layer is substantially lattice matched tothe magnesium oxide tunnel layer. A metal oxide layer may be present onthe opposite surface of the crystalline free layer to provide an oxideinterface on opposing surfaces of the crystalline free layer in order togenerate perpendicular magnetic anisotropy character.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a side cross-sectional view depicting one embodiment offorming a material stack including a free layer of an alloy of cobalt(Co), iron (Fe) and boron (B) overlying a reference layer, and a metallayer comprising a boron (B) sink composition may be deposited atop thefree layer, in accordance with the present disclosure.

FIG. 2 is a side cross-sectional view depicting an anneal process todiffuse boron (B) from the free layer to the metal layer comprising theboron sink composition, in accordance with the present disclosure.

FIG. 3A is a side cross-sectional view depicting one embodiment ofetching a portion of the metal layer including the boron (B) sinkcomposition from the structure depicted in FIG. 2.

FIG. 3B is a side cross-sectional view depicting one embodiment ofremoving an entirety of the metal layer including the boron (B) sinkcomposition from the structure depicted in FIG. 2.

FIG. 4A is a side cross-sectional view depicting forming a regrowthmetal layer on the remaining portion of the metal layer including theboron (B) sink composition that is depicted in FIG. 3A.

FIG. 4B is a side cross-sectional view depicting forming a cobalt (Co)and iron (Fe) containing alloy on the free layer that is depicted inFIG. 3B, in accordance with one embodiment of the present disclosure.

FIG. 5A is a side cross-sectional view depicting forming a metal oxideatop the free layer that is depicted in FIG. 4A, wherein the free layercomprises a crystalline cobalt and iron alloy and an interface betweenthe metal oxide and free layer provides perpendicular magneticanisotropy character.

FIG. 5B is a side cross-sectional view depicting forming a metal oxideatop the cobalt (Co) and iron (Fe) containing alloy that is depicted inFIG. 4B, wherein the free layer comprises a crystalline cobalt and ironalloy and an interface between the metal oxide and free layer providesperpendicular magnetic anisotropy character.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure. Forpurposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the embodiments of the disclosure,as it is oriented in the drawing figures. The terms “positioned on”means that a first element, such as a first structure, is present on asecond element, such as a second structure, wherein interveningelements, such as an interface structure, e.g. interface layer, may bepresent between the first element and the second element. The term“direct contact” means that a first element, such as a first structure,and a second element, such as a second structure, are connected withoutany intermediary conducting, insulating or semiconductor layers at theinterface of the two elements.

As used herein, the term “memory device” means a structure in which theelectrical state can be altered and then retained in the altered state,in this way a bit of information can be stored. Spin torque transfermagnetic random access memory (STT MRAM) uses magnetic materials as thememory storage element. In some examples, STT MRAM uses memory storageelements that take advantage of the effect in which a current that ispassed through a magnetic material, such as a magnetic tunnel junction(MTJ)—reverses its direction of magnetization. Passing a current throughthe MTJ causes its direction of magnetization to switch between aparallel or anti-parallel state, which has the effect of switchingbetween low resistance and high resistance. Because this can be used torepresent the 1s and 0s of digital information, STT MRAM can be used asa non-volatile memory.

Reading STT MRAM involves applying a voltage to the MTJ to discoverwhether the MTJ offers high resistance to current (“1”) or low (“0”).Typically, a MTJ stack includes reference layer(s) (also referred to aspinned layer), tunnel layer(s) and free layer(s). A typical MTJ stack isusually configured such that the reference layer and tunnel barrier aredisposed beneath the free layer. It should be noted that exemplarymaterials for the free layer(s) include alloys and/or multilayers of Fe,Ni, Co, Cr, V, Mn, Pd, Pt, B, O and/or N. Further, the referencelayer(s) can be composed of alloys and/or multilayers of Fe, Ni, Co, Cr,B, Mn, Pt, Pd, Ru, Ta, W and/or Cu. Moreover, the tunnel barrierlayer(s) can be composed of MgO, Al₂O₃, TiO₂, or materials of higherelectrical tunnel conductance, such as semiconductors or low-bandgapinsulators. A spin torque MRAM uses a 2 terminal device with a pinnedlayer, tunnel barrier, and free layer in a magnetic tunnel junctionstack. The magnetization of the pinned layer is fixed in direction (saypointing up) and a current passed down through the junction makes thefree layer parallel to the pinned layer, while a current passed upthrough the junction makes the free layer anti-parallel to the pinnedlayer. A smaller current (of either polarity) is used to read theresistance of the device, which depends on the relative orientations ofthe magnetizations of the free and pinned layers. The resistance istypically higher when the magnetizations are anti-parallel, and lowerwhen they are parallel (though this can be reversed, depending on thematerial).

Cobalt iron boride (CoFeB) with double oxide interfaces has been shownto be free layer material for STT-MRAM applications. In this materialsystem, the perpendicular magnetic anisotropy (PMA) performance isgenerated from both of the oxide interfaces, with one being the tunnelbarrier layer, e.g., an interface with a magnesium oxide (MgO) tunnelbarrier layer. The other oxide layer being a cap or seed can be variousdifferent kinds of oxide, for example, MgO, MgTiOx, MgTaOx, Ti oxide andTa oxide, etc. Reference layers and free layers of PerpendicularMagnetic Anisotropy (PMA) STT MRAMs have magnetic moments that areperpendicular to the wafer plane.

In accordance with the methods and structures of the present disclosure,compared to tantalum (Ta) capped free layer, free layers with doubleoxide interfaces showed stronger PMA and lower damping, thus betterswitching performance. However, it has been determined that an oxide capis not as good a boron (B) sinking material as a metal cap, for examplea tantalum (Ta) metal cap, which can hurt both tunnel magnetoresistance(TMR) and free layer exchange stiffness. High TMR is desired for readoperations in memory devices, such as STT MRAM devices. High exchangestiffness is beneficial for greater than sub 20 nm small devices.

In some embodiments, the present disclosure provides a method to improveTMR and free layer exchange stiffness in stacks where the free layer hasdouble oxide interfaces. In some embodiments, the method includesforming a cobalt iron boride (CoFeB) based magnetic layer capped with ametal layer that acts as a boron (B) sink during subsequent annealingprocesses. As will be described in greater detail below, some metalssuitable for use in the metal layer used as the boron (B) sink caninclude titanium (Ti), tantalum (Ta), zirconia (Zr) and alloy thereof.In a following anneal process, the boron (B) from the free layer ofCoFeB diffuses into a top metal layer and leaves crystalline cobalt iron(CoFe) alloys as the magnetic free layer. In some embodiments, theformation of the crystalline cobalt iron alloy improves the exchangestiffness of the free layer. In a following process step, an in situetch back process removes at least a portion of the metal layer thatprovides the boron sink, which removes a portion of the boron that hasdiffused to the metal layer. A metal oxide may then be formed, which caninclude a remaining portion of the metal layer, which gives rise to PMA.In some embodiments prior to forming the metal oxide layer, a metallayer may be deposited, such as CoFe, Fe or CoFeB, and then a layer ofoxide can be formed by RF sputtering. This can allow the free layer tocrystallize from the barrier interface for high TMR and can also improvethe free layer exchange stiffness, as the B content decreases in thefree layer. Further details of the methods and structures of the presentdisclosure are discussed blow with reference to FIGS. 1-5B.

FIG. 1 depicts one embodiment of forming a material stack 50 including afree layer 20 of an alloy of cobalt (Co), iron (Fe) and boron (B)overlying a reference layer 10, and a metal layer 25 comprising a boron(B) sink composition may be deposited atop the free layer 20.

The reference layer 10 may be composed of any magnetic material that canhave a magnetic direction that can be fixed, e.g., to provide a fixed orpinned magnetic direction for use the in the reference layer 10 of amemory device, e.g., STT MRAM device. In some examples, the referencelayer 10 may be composed of alloys of Fe, Ni, Co, Cr, B, Mn, Pt, Pd, Ru,Ta, W and/or Cu combined with a multilayer structure made of alternatinglayers of Co, Ni, Pt, Pd, Ir and Ru etc with strong perpendicularmagnetic anisotropy or alloys with strong perpendicular anisotropy, suchas CoFeTb, CoFeGd or CoCrPt, CoPt, CoPd, FePt, FePd. The reference layer10 may be composed of a single material layer or may be composed ofmultiple material layers. In some embodiments, the reference layer 10may have a thickness ranging from 15 Å to 200 Å. Although not depictedin the supplied figures, the reference layer 10 may be formed on anelectrically conductive electrode, or may be present on a substrate. Thereference layer 10 can be formed using a deposition method, such asphysical vapor deposition (PVD), e.g., plating, electroless plating,electroplating, sputtering and combinations thereof. In otherembodiments, the reference layer 10 may be deposited using chemicalvapor deposition (CVD).

A tunnel barrier layer 15 is present between the reference layer 10 andthe free layer 20 of the alloy of cobalt (Co), iron (Fe) and boron (B).The tunnel barrier layer 15 may be hereafter referred to as a metaloxide layer 15, and may have a thickness to promote tunneling. The metaloxide layer 15 in combination with the reference layer 10 may produce aspin torque that can change the direction of magnetization in the freelayer 20 of the alloy of cobalt (Co), iron (Fe), and boron (B), in whichdirectional changes in the magnetization direction of the free layer isone mechanism that can provide the memory functions of a STT MRAM. Insome embodiments, when the metal oxide layer 15 is a magnesium oxidecontaining layer, the metal oxide layer 15 may be magnesium oxide (MgO).It is noted that the above compositions for the metal oxide layer 15have been provided for illustrative purposes, and it is not intended tolimit the scope of the present disclosure to only these materials. Forexample, in some instances, the tunnel barrier layer provided by themetal oxide layer 15 can be composed of Al₂O₃, TiO₂, and combinationsthereof. The metal oxide layer 15 may have a thickness ranging from 5 Åto 20 Å. The metal oxide layer 15 may be formed using a depositiontechnique, such as physical vapor deposition (PVD), e.g., plating,electroless plating, electroplating, sputtering and combinationsthereof, or chemical vapor deposition, such as metal organic chemicalvapor deposition (MOCVD) or plasma enhanced chemical vapor deposition(PECVD).

The free layer 20 that is composed of the alloy of cobalt (Co), iron(Fe) and boron (B) may have a magnetic direction that can be switched ina manner that can provide a memory mechanism for STT MRAMs. In someembodiments, the free layer 20 that is composed of an alloy of cobalt(Co), iron (Fe), and boron (B) may have the composition of Co₆₀Fe₂₀B₂₀.It is noted that this is only one example of an alloy of cobalt (Co),iron (Fe) and boron (B) that can provide the free layer 20. Othercompositions are equally suitable for the free layer 20 that is composedof the alloy of cobalt (Co), iron (Fe) and boron (B). It is noted thatprior to the following described anneal process the boron (B) of thefree layer 20 that is composed of the alloy of cobalt (Co), iron (Fe)and boron (B) is greater than 15 at. %. For example, the boron contentmay range from 15 at. % to 30 at. % in the free layer that is composedof the alloy of cobalt (Co), iron (Fe), and boron (B) prior to the belowdescribed anneal process. In other examples, the boron content may rangefrom 20 at. % to 25 at. % in the free layer that is composed of thealloy of cobalt (Co), iron (Fe), and boron (B) prior to the annealprocess.

As will be discussed below, the boron (B) concentration of the freelayer 20 will be reduced by the annealing to diffuse the boron (B) fromthe free layer 20 that is composed of cobalt (Co), iron (Fe) and boron(B) in to the metal layer 25 that acts as a boron (B) sink.

The free layer 20 that is composed of the alloy of cobalt (Co), iron(Fe) and boron (B) may be formed using a deposition process, such asphysical vapor deposition (PVD), which can include sputtering, plasmaenhanced chemical vapor deposition (PECVD), metal organic chemical vapordeposition (MOCVD) and combinations thereof. The free layer 20 may havea thickness ranging from 5 Å to 30 Å. In another embodiment, the freelayer 20 may have a thickness ranging from 10 Å to 20 Å. In one example,the free layer 20 may have a thickness of 15 Å.

In some embodiments, the first step of a process flow in accordance withthe present disclosure is to grow the CoFeB based magnetic layer (alsoreferred to as a free layer 20 of an alloy of cobalt (Co), iron (Fe) andboron (B)) capped with a relatively thick metal layer (also referred toas a metal layer 25 comprising a boron (B) sink composition). Forexample, by relatively thick it can be meant that the thickness of themetal layer 25 including the boron (B) sink composition may range from 5Å to 25 Å. In another embodiment, the metal layer 25 including the boron(B) sink composition may range from 10 Å to 20 Å. In one example, themetal layer 25 including boron (B) sink composition may have a thicknessof 15 Å.

In some embodiments, the metal layer 25 acts as a boron (B) sink duringthe subsequent annealing process that is described below. By “boron (B)sink” it is meant that the material attracts boron (B) that is diffusingfrom the free layer 20 of an alloy of cobalt (Co), iron (Fe) and boron(B), in which the boron diffuses into the boron (B) sink material. Someexamples of metals that are suitable for the metal layer 25 includingthe boron (B) sink composition include titanium (Ti), tantalum (Ta),zirconium (Zr) or alloys containing those. In one example, the metallayer 25 is composed of tantalum (Ta) that is formed directly on a freelayer 20 of CoFeB. It is noted that the above list of metal compositionsfor the metal layer 25 that acts as a boron (B) sink is provided forillustrative materials only, and is not intended to limit the presentdisclosure, as other materials are equally suitable, so long as borondiffused to the material composition selected, as part of the followingdescribed method.

The metal layer 25 that acts as the boron (B) may be formed using adeposition process, such as physical vapor deposition (PVD), e.g.,plating, electroplating, electroless plating, sputtering andcombinations thereof.

FIG. 2 depicts an anneal step 5 to diffuse boron (B) from the free layer20 to the metal layer 25 comprising the boron (B) sink composition. Whatcan be referred to as the second step of the method described withreference to FIGS. 1-5B, is an in-situ anneal step 5 at temperaturesgreater than 300° C. for greater than 10 minutes. The term “in-situ”means that there is no breaking of vacuum during the annealing betweenthe formation of the metal layer 25 and the anneal step 5. For example,the annealing can be done in the different chambers of the same toolwhich was kept under vacuum, vs taking the wafer out of the tool,exposed to air and anneal in a different tool. During the anneal step 5,the boron (B) is expected to diffuse from the free layer 20 of thecobalt (Co), iron (Fe) and boron (B) to the metal layer 25 comprisingthe boron (B) sink composition, leaving crystalline CoFe as the magneticfree layer 20 a. As used herein, the term crystalline denotes a materialcomposed of a single crystal or polycrystalline crystal structure.

In some embodiments, the anneal step 5 may be at a temperature rangingfrom 300° C. to 600° C. In other embodiments, the anneal step 5 may beat a temperature ranging from 325° C. to 575° C. In yet otherembodiments, the anneal step 5 may be at a temperature ranging from 350°C. to 550° C. In yet an even further embodiment, the anneal step 5 maybe at a temperature ranging from 375° C. to 525° C.

The anneal step 5 can be for a time period ranging from 5 minutes to 30minutes. In some embodiments, the anneal step 5 may range from 10minutes to 20 minutes. In yet another embodiment, the anneal step 5 maybe equal to 15 minutes. The above examples of anneal time are providedfor illustrative purposes and are not intended to limit the presentdisclosure. For example, the anneal time may be modified in view of theselected anneal temperature.

The boron (B) in the free layer 20 of the alloy of cobalt (Co), iron(Fe) and boron (B) diffuses to the metal layer 25 comprising the boron(B) sink composition, wherein following the anneal process the boron (B)content in the free layer 20 a of the cobalt (Co), iron (Fe) and boron(B) may be reduced to be less than 15 at. %. In some examples, theamount of boron (B) that is present in the free layer 20 a of the alloyof cobalt (Co), iron (Fe) and boron (B) after the anneal process may beequal to 15 at. %, 14 at. %, 13 at. %, 12 at. %, 11 at. %, 10 at. %, 9at. %, 8 at. %, 7 at. %, 6 at. %, 5 at. %, 4 at. %, 3 at. %, 2 at. %, or1 at. % or any range therebetween (e.g., 15 at. % to 10 at. %, 10 at. %to 5 at. %, 5 at. % to 1 at. %), or between any of the foregoing values.In one embodiment, the boron (B) in the free layer 20 may be completelyremoved so that after the anneal, the boron content of the free layer 20a may be 0 at. %. For example, following the anneal, the composition ofthe free layer 20 a may be equal to Co₇₅Fe₂₅.

Removing the at least a portion of boron (B) (and in some instancesboron in its' entirety) from the free layer 20 of the cobalt (Co), iron(Fe) and boron (B) improves the exchange stiffness of the free layer 20.In one embodiment, following the anneal step, the exchange stiffness ofthe free layer may range from 5 pJ/m to 40 pJ/m. In another embodiment,following the anneal step, the exchange stiffness of the free layer mayrange from 8 pJ/m to 20 pJ/m.

In some embodiments, only a portion of the boron (B) in the free layer20 of the alloy of cobalt (Co), iron (Fe) and boron (B) is converted tohigh stiffness crystalline material, wherein boron (B) may remain in aportion of the free layer 20.

The boron (B) that diffused into the metal layer 25 comprising the boron(B) sink composition may increase the boron (B) in the metal layer 25 ato be greater than 5 at. %. In some other embodiments, the boron (B)content that is diffused into the metal layer 25 a may be greater than10 at. %. In some examples, the amount of boron (B) that is present inthe metal layer 25 a after anneal process may be equal to 1 at. %, 2 at.%, 3 at. %, 4 at. %, 5 at. %, 6 at. %, 7 at. %, 8 at. %, 9 at. %, 10 at.%, 11 at. %, 12 at. %, 13 at. %, 14 at. %, or 15 at. % or any rangetherebetween (e.g., 1 at. % to 5 at. %, 5 at. % to 10 at. %, 10 at. % to15 at. %), or between any of the foregoing values.

FIG. 3A depicts one embodiment of etching a portion of the metal layer25 a including the boron (B) sink composition that the boron (B) fromthe free layer 20 a has diffused to. Etching this portion can remove theboron (B) from the structure. In some embodiments, the etch process onlyremoves a portion of the metal layer 25 a, wherein a remaining portionof the metal layer 25 b is present on the free layer 20 a having areduced thickness. For example, the thickness of the free layer 20 a canbe reduced to ¾ to ¼ its original thickness. In another example, thethickness of the free layer 20 a can be equal to ½ its thickness. Insome embodiments, the etch process may be an in-situ etch back process,in which the remaining portion of the metal layer 25 b may range from 2Å to 6 Å in thickness.

FIG. 3B depicts another embodiment of the present disclosure, in whichthe etch process removes an entirety of the metal layer 25 including theboron (B) sink composition from the structure depicted in FIG. 2. Inthis embodiment, the etch process may be continued to remove an entiretyof the metal layer 25 including the boron that diffused into the metallayer 25 from the free layer 20 a, as well as etching a portion of thefree layer 20 a. In this embodiment, the etch process may etching intothe free layer 20 a to a depth ranging up to 5 Å. The etch process foretching the free layer 20 a after removing an entirety of the metallayer 25 may be any of the aforementioned anisotropic or isotropic etchprocesses.

FIG. 4A depicts one embodiment of forming a regrowth metal layer 30 onthe remaining portion of the metal layer 25 b including the boron (B)sink composition that is depicted in FIG. 3A. In this embodiment, theregrowth metal layer 30 begins the process for forming a metal oxidelayer 40 atop the free layer 20 a, as depicted in FIG. 5A. The regrowthmetal layer 30 may have the same composition as the remaining portion ofthe metal layer 25 b including the boron (B) sink composition. Forexample, when the remaining portion of the metal layer 25 b is composedof tantalum (Ta), the regrowth metal layer 30 may also be composed oftantalum (Ta). The regrowth metal layer 30 may also be composed of adifferent composition material than the remaining portion of the metallayer 25 b. It is noted that tantalum (Ta) is only one example of amaterial layer that may be suitable for the regrowth metal layer 30.Other material layers that can be suitable for the regrowth metal layer30 include titanium (Ti), tantalum (Ta), zirconium (Zr) or alloyscontaining those elements. The regrowth metal layer 30 may be depositedusing a physical vapor deposition (PVD) or chemical vapor depositionmethod (CVD). For example, the regrowth metal layer 30 may be formedusing plating, electroplating, electroless plating, sputtering, plasmaenhanced chemical vapor deposition, metal organic chemical vapordeposition, and combinations thereof. The regrowth metal layer 30 may bedeposited to a thickness as great as 10 Å. In other embodiments, theregrowth metal layer 30 can be deposited to a thickness ranging from 1 Åto 5 Å.

FIG. 4B depicts another embodiment of the present disclosure, in whichan iron (Fe) containing metal layer 35 is formed on the recessedremaining portion on the free layer 20 b that is depicted in FIG. 3B. Inone example, the iron containing metal layer 35 may be crystalline CoFe.In other examples, the iron containing alloy can be CoFeB, and may alsobe entirety composed iron (Fe).

In this embodiment, the iron (Fe) containing metal layer 35 is formed onthe recessed remaining portion on the free layer 20 b that is eitherentirely free of boron (B), e.g., is a cobalt (Co) and iron (Fe)crystalline material, or is crystalline cobalt (Co), iron (Fe) and boron(B) containing alloy that has a reduced boron concentration resultingfrom the outdiffusion methods described above. The iron (Fe) containingmetal layer 35 may be formed using a deposition method, such as physicalvapor deposition or chemical vapor deposition. For example, the iron(Fe) containing metal layer 35 may be deposited using plating,electroplating, electroless plating, sputtering, plasma enhancedchemical vapor deposition, metal organic chemical vapor deposition, andcombinations thereof. The iron (Fe) containing metal layer 35 may bedeposited to a thickness as great as 10 Å. In other embodiments, theiron (Fe) containing metal layer 35 can be deposited to a thicknessranging from 1 Å to 5 Å.

Still referring to FIG. 4B, a regrowth metal layer 30 may be formed onthe iron (Fe) containing metal layer 35. In this embodiment, theregrowth metal layer 30 may also be composed of titanium (Ti), tantalum(Ta), zirconium (Zr) or alloys containing those elements. The regrowthmetal layer 30 may be deposited using a physical vapor deposition (PVD)or chemical vapor deposition method (CVD). For example, the regrowthmetal layer 30 may be formed using plating, electroplating, electrolessplating, sputtering, plasma enhanced chemical vapor deposition, metalorganic chemical vapor deposition, and combinations thereof. Theregrowth metal layer 30 may be deposited to a thickness as great as 10Å. In other embodiments, the regrowth metal layer 30 can be deposited toa thickness ranging from 1 Å to 5 Å.

FIG. 5A depicts forming a metal oxide 40 atop the free layer 20 a thatis depicted in FIG. 4A. FIG. 5B depicts forming a metal oxide atop thecobalt (Co) and iron (Fe) containing alloy that is depicted in FIG. 4B.The formation of the metal oxide 40 may result from exposing to anoxygen containing atmosphere or oxygen plasma. Referring to FIGS. 5A and5B, an oxidation step may then be performed, which gives rise toperpendicular magnetic anisotropy (PMA). For stack shown in FIG. 4B andFIG. 5B, it is also possible to only grow the 0-5 Å CoFe, Fe or CoFeBand then a layer of oxide by RF sputtering. This will allow the freelayer 20 a to crystallize from the barrier interface for high tunnelmagnetic resonance (TMR), and also improve the free layer 20 a exchangestiffness, as the boron (B) content decreases in the free layer 20 a.

In this embodiment, the free layer 20 a comprises a crystalline cobaltand iron alloy, and an interface between the metal oxide layer 15 andthe free layer provides perpendicular magnetic anisotropy character.

In some embodiments, another reference layer (also referred to as pinnedlayer, may be formed atop the metal oxide layer 40 that is depicted inFIGS. 5A and 5B. The above description of the reference layer identifiedby reference number 10 is suitable for the description of the referencelayer that is depicted in FIGS. 5A and 5B.

In another aspect, a memory device is provided that includes a magnesiumoxide tunnel layer atop a reference layer, and a crystalline free layercomprised of cobalt and iron alloy that is substantially free of boron,wherein the crystalline free layer is substantially lattice matched tothe magnesium oxide tunnel layer. A metal oxide layer may be present onthe opposite surface of the crystalline free layer to provide an oxideinterface on opposing surfaces of the crystalline free layer in order togenerate perpendicular magnetic anisotropy character.

The methods and structures that have been described above with referenceto FIGS. 1-5A may be employed in any electrical device. For example, thememory devices that are disclosed herein may be present withinelectrical devices that employ semiconductors that are present withinintegrated circuit chips. The integrated circuit chips including thedisclosed interconnects may be integrated with other chips, discretecircuit elements, and/or other signal processing devices as part ofeither (a) an intermediate product, such as a motherboard, or (b) an endproduct. The end product can be any product that includes integratedcircuit chips, including computer products or devices having a display,a keyboard or other input device, and a central processor.

It should be further understood that STT MRAM devices according to thepresent principles can be employed in any computing apparatus thatutilizes RAM. For example, such computing apparatuses can utilize theSTT MRAM devices in lieu of or in addition to RAM. Such computingapparatuses can include personal computers, mainframes, laptops, smartphones, tablet computers and other computing devices.

Having described preferred embodiments of STT MRAM devices, apparatusesand manufacturing methods (which are intended to be illustrative and notlimiting), it is noted that modifications and variations can be made bypersons skilled in the art in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A method for forming a memory device comprising:providing a single free layer of an alloy of at least one of cobalt(Co), iron (Fe) and boron (B) atop a reference layer; depositing a metallayer comprising a boron (B) sink composition atop the free layer;annealing to diffuse boron (B) from the free layer to the metal layercomprising the boron sink composition, wherein the depositing the metallayer and the annealing to diffuse boron from the free layer to themetal layer is conducted in situ, the annealing having a durationranging from 15 minutes to 30 minutes; removing the metal layerincluding the boron (B) sink composition, the remaining composition ofthe single free layer is said cobalt (Co) and said iron (Fe) that iscrystalline and from which boron (B) has been removed; forming an ironcontaining metal layer of cobalt ferrite (CoFe) in direct contact withan exposed surface of the free layer; and forming a metal oxide atop theregrowth metal layer, wherein the free layer comprises a crystallinecobalt and iron alloy and an interface between the metal oxide and freelayer provides perpendicular magnetic anisotropy character.
 2. Themethod of claim 1, wherein the free layer comprises CoFeB.
 3. The methodof claim 2, wherein the free layer is present atop a metal oxide layerthat is present atop the reference layer.
 4. The method of claim 3,wherein the metal oxide layer comprises magnesium oxide and thereference layer comprises at least one of Fe, Ni, Co, Cr, V, Mn, Pd, Pt,B, O and N.
 5. The method of claim 1, wherein the boron sink compositioncomprises titanium (Ti), tantalum (Ta), zirconium (Zr) or alloysthereof.
 6. The method of claim 1, wherein said forming the metal oxideatop the free layer comprises exposure to oxygen, oxygen plasma or RFsputtering.
 7. The method of claim 1, wherein the removing of the metallayer including the boron (B) sink composition comprises etching.
 8. Themethod of claim 1, wherein the iron containing metal layer comprisescobalt and iron.
 9. The method of claim 1, wherein the iron containingmetal layer is crystalline.
 10. The method of claim 1, wherein followingsaid annealing to diffuse boron (B) from the free layer to the metallayer comprising the boron sink composition, the free layer comprisedCoFe.
 11. A memory device comprising: a single crystalline free layercomprised of a cobalt and iron alloy that is substantially free ofboron, wherein the single crystalline free layer is in overlying areference layer; a regrowth metal layer on a surface of the singlecrystalline free layer, wherein the regrowth metal layer is comprised ofcobalt ferrite (CoFe); and a metal oxide layer zirconium oxide (ZrO)present on the regrowth metal layer to provide an oxide interface onopposing surfaces of the single crystalline free layer in order togenerate perpendicular magnetic anisotropy character.
 12. The memorydevice of claim 11, wherein the single crystalline free layer is CoFe.13. The memory device of claim 11, wherein the single crystalline freelayer has a thickness ranging from 5 Å to 30 Å.
 14. The memory device ofclaim 11, wherein the reference layer comprises a material selected fromthe group consisting of Fe, Ni, Co, Cr, V, Mn, Pd, Pt, B, O and N. 15.The memory device of claim 11, wherein the metal oxide layer is selectedfrom the group consisting of aluminum oxide (Al₂O₃), titanium dioxide(TiO₂) and combinations thereof.
 16. The memory device of claim 15,wherein the metal oxide layer has a thickness ranging from 5 Å to 20 Å.17. A memory device comprising: a single crystalline free layercomprised of a cobalt and iron alloy that is substantially free ofboron; a regrowth metal layer on a surface of the single free layer,wherein the regrowth metal layer is comprised of cobalt ferrite (CoFe);and a metal oxide layer present on a surface of the single crystallinefree layer in order to generate perpendicular magnetic anisotropycharacter in a metal stack for a spin torque transfer magnetic randomaccess memory device.
 18. The memory device of claim 17, wherein themetal stack includes a first metal oxide layer in direct contact with afirst side of the single crystalline free layer, and a second metaloxide layer in direct contact with the regrowth metal layer on a secondside of the single crystalline free layer.
 19. The memory device ofclaim 17, wherein the single crystalline free layer is CoFe.
 20. Thememory device of claim 18, wherein the single crystalline free layer hasa thickness ranging from 5 Å to 30 Å.